1. Field of the Invention
This invention relates to the field of neuroscience and more particularly relates to the application of human brain wave analysis including quantitative electroencephalography. More particularly, the present invention relates to conceptual interpreters and conceptually driven interfaces.
2. Discussion of the Background
Electrical brain activity can be detected using electrodes placed on the scalp of a human subject. An electroencephalogram (EEG) is a recording of a time-varying spontaneous potential (SP) that is obtained from an alert and resting subject. When a subject is presented brief sensory stimuli (e.g., a flash, a click, a mild shock to the skin), a time-varying evoked potential (EP) is superimposed upon the normally present SP so that the EEG voltage includes both SP and EP components. The EP waveform begins within a few milliseconds after receipt of a sensory stimulus, and continues with a decreasing oscillatory magnitude so that it can be distinguished from the SP for as long as one second.
Previous investigations of EP signals have been directed toward methods and devices for distinguishing between normal subjects and subjects with various brain dysfunctions and for use of EP signals to control hardware devices.
Various regions of the brain have different functions and some of those regions are responsible for different types of conceptual functions, such as spatial relationship and word interpretation. When one of those areas of the brain dysfunctions, the specific mental functions associated therewith are impaired.
U.S. Pat. No. 3,901,215 discloses selection of stimuli that are intended to generate different levels of brain function, such as sensory, perceptual, and conceptual function. A neurometric test battery is disclosed in the '215 patent. That test battery includes several stimulus conditions that represent different levels of stimulus complexity. For each stimulus condition, the disclosed neurometric test battery attempts to determine whether the brain of a subject, as indicated by EP waveforms, distinguishes between two exemplars of a similar type. The model used in the '215 patent assumes, however, only that a difference in EP signals received from the brain of a subject while that subject senses different stimuli indicates that the brain of the subject has distinguished between those stimuli. Therefore, the only answer obtainable based upon the model disclosed in the '215 patent is that two stimulus conditions are either the same or different.
U.S. Pat. No. 4,926,969 discloses an EP based control device in which a subject must focus attention on one checkerboard stimulus among a panel of such stimuli. Those stimuli are used to stimulate the receptor system of a subject at different frequencies. When the subject focuses attention on one of the panels, the unique frequency associated with that panel generates a unique EP waveform from the brain of the subject. The unique frequency dependence generated thereby is used to selectively control a hardware device. Different commands may be issued to the device depending upon which checkerboard the subject stares at. Using that system, the subject must attend to a computer display representing a desired control command. The '969 patent explicitly (see column 8, lines 34-41) avoids using complex stimuli such as size, color, and shape.